Place Beef Tenderloin on wire rack and sprinkle coarse kosher salt liberally on all sides. Refrigerate on lowest shelf uncovered overnight. Remove from fridge 1 hour before cooking.
Mix all ingredients for the roasted vegetables and set aside.
Preheat oven to 250°F. Mix all beef rub ingredients, brush tenderloin with dijon and spread spice rub over top and sides of beef.
Place beef in oven and roast until thermometer in thickest part reads 115°F, or about 2 hours. Remove from oven and set aside. Let rest at room temperature for up to 2 hours or refrigerate it again until you are ready for Step 7. Make sure to bring it back to room temperature before completing the roasting.
Preheat oven to 425°F
Spread vegetables on sheet tray in a single layer, and roast in oven until fork-tender and slightly browned, or about 25 minutes. Remove from oven and set aside. These can be served immediately or reheated later with a little olive oil or butter, and will be just as good!
Place beef back in 425°F preheated oven and roast for another 10-15 minutes. Remove when thermometer inserted in the thickest part reads 125°F.
Let beef rest for at least 20 minutes before slicing and serving.